In a semiconductor device, it is effective to use a material having a high critical electric field in order to realize a high breakdown voltage and a low on resistance. Since a nitride semiconductor has a high intensity of the critical electric field, the semiconductor device realizing the high breakdown voltage and the low on resistance is achieved by using the nitride semiconductor.
In the nitride semiconductor device, as a method of increasing an avalanche capability, a method of connecting a source electrode to a substrate, or alternatively a method using a p-type GaN layer or using a layer structure in which a two-dimensional hole gas is generated is employed.